Improving Halfwave Rectifier Question

[kramps]

I have an old St. George US made amp that has a halfwave rectifier and would like to improve it. Does anybody have suggestions or know of this amp company. There is no info out there except a Harmony Central review of this same amp. Thanks for any assistance with this.


http://reviews.harmony-central.com/r...4+Valiant/10/1

kramps

[Rob Mercure]

What's the tube compliment of this amp. As best I know all of the amps made since WWII with a 1/2 wave tube rectifier were "line connected" so I hope you know the risks involved in using these amps and the precautions necessary. Not kidding - life or death shock possibility here. Now if this amp is somehow different ignore my cautions so please let us know what the tube types are and we'll help you "improve" it.

Rob

[kramps]

St George Tube Lineup

That would have been my thoughts as well but the tubes are 6BM8 for power and PI a 6GW8 for trem and a 12AX7 for preamp unless I have them in the wrong order. The HC review of this amp says it has a 60 cycle hum which it would with a halfwave rectifier. It's similar to the rectifier in a Fender reverb unit.

kramps

[Enzo]

Yes, 60Hz hum would result from weak filteration in a half wave supply. But more than that, 60Hz hum can easily come from improper or nonexistent grounding, from pick up of radiated noise, from ground loops. Set your meter to AC volts and measure the B+. The AC you read is its ripple.

[Rob Mercure]

The only other thought is that if this amp for some reason is fixed bias - seems too low powered though - is that the bias supply is 1/2 wave and providing your 60 Hz hum. If so it's gotta be the filter. Or perhaps, in addition to leakage as Enzo mentions, perhaps a heater to cathode short in one of the tubes (heater supply 60 Hz).

Rob

[Enzo]

Does YOURS also hum? Or just the one reviewed? And we should not infer that ONE amp with a symptom means ALL of them have it for the same reason.

[kramps]

Here's The Story

I just moved to a different state and brought the last load down. In it I found I had this little funky amp with no tubes but a power and output transformer and three nine pin sockets. I looked at the rectifer and found it was half wave. I'd had a discussion with another amp builder before I moved about US made ST Geoge amps and when I stumbled on to this little bugger it looked very much like his description and it's not Japanese. I checked the internet and the only thing I found was the HC review I posted earlier. It gave the lineup of tubes but the order I put them in was a an estimated guess on my part from all of the amps I have worked on. The reviewer's amp had a 60 cycle hum and I as of yet have not fired this one up do to other pressing commitments but in reading up on half wave rectifers I always seem to find reference to the same 60 cycle hum. I was just looking to see if I could improve on the rectifier before I did fire it up.

[kramps]

Full Wave Bridge Rectifier

Is there any reason why I couldn't rewire the circuit as a full wave bridge rectifier since there isn't a center tap at my disposal? And with the 3 tubes the amp uses does it look like I have them in the right order?

Thanks,
kramps